Convertible composite engine

ABSTRACT

A convertible composite engine capable of either shaft horsepower or thrust generation and split-powered operation in which partial thrust and partial shaft horsepower is generated. The engine is concentric about a single centerline and includes two coaxial free turbines, one driving a load such as by-pass fan and the other a shaft horsepower take-off, such as is commonly used to drive a helicopter rotor drive shaft. A single gas generator provides compressed and heated gases to the coaxial free turbines with the total amount of gases provided determined by the total power required from the two free turbines and the split of gas flow through each free turbine determined by the position of the variable inlet guide vanes at the inlet to each turbine.

United States Patent Shohct et al.

[451 July 25, 1972 [54] CONVERTIBLE COMPOSITE ENGINE [72] Inventors:Herbert N. Shohet, Norwalk; Joseph L. Magi-l; Edward R. Prlnuchuk, bothof 2| Appl. No.: 53,113

[52] US. Cl 60/2Z6, 415/68, 417/408, 244/7, 244/53, 60/39.33, 60/3915,60/3918, 60/39. 1 7, 60/239, 60/263, 415/61 3,514,952 6/1970 Schumacher..60/39. 1 6 X 3,306,036 2/1967 Wooler ..60/39.16 3,423,048 1/1969Clarke .....60/39. 16 X 3,449,914 6/1969 Brown ..60/39.16 X

Primary Examiner-Carlton R. Croyle Assistant Examiner-Robert 5. GarrettAttorney-Vernon F. Hauschild [57] ABSTRACT A convertible compositeengine capable of either shaft horsepower or thrust generation andsplit-powered operation in which partial thrust and partial shafthorsepower is generated, The engine is concentric about a singlecenterline and in- [51 Int. Cl. ..F02c 7/02 dudes two coaxial freeturbines one i i a |oad such as Field of Search ...............60/39.l6,39.17, 39.33, 39.25, pass fan and the other a n horsepower takeoff suchas is 60/226 3915 g 3 127; commonly used to drive a helicopter rotordrive shaft. A single /4 244/7 6 gas generator provides compressed andheated gases to the coaxial free turbines with the total amount of gasesprovided [56] References Cited determined by the total power requiredfrom the two free tur- UNITED ATES PATENTS bines and the split of gasflow through each free turbine determined by the position of thevariable inlet guide vanes at the 3,465,526 9/1969 Ernerick ..60/39. [6x inlet each whim 3,472,487 10/1969 Moc11mann ..60/39.16 X 3,520,1337/1970 Fox ..60/39.l6 X 17 Chim,4Drawing Figures Z8 fla /4 4% 1.3 J5 a aM 4! f 4 a .74 J6 zz I 6 J2 95 /Z 50 g .2? 6 5a 74 Z0 71 Patented July25, 1972 2 Sheets-Sheet l 1 w WW MHZ Dim \wv Q? my w r 6;. 5 z MJ VM W7g 5 M RQ lm Rm S Q )Q NOE Patented July 25, 1972 2 Sheets-Sheet 2CONVERTIBLE COMPOSITE ENGINE CROSS-REFERENCE TO RELATED APPLICATIONS Anapplication in the name of Herbert N. Shohet and Joseph L. Magrientitled Convertible Composite Engine Control" is being filed on evendate and claims the control system disclosed herein.

BACKGROUND OF THE INVENTION 1. Field of Invention This invention relatesto convertible composite engines which are capable of operating in athrust generating or shaft horsepower mode of operation and which arealso capable of a split power form of operation in which, typically, aportion of the power generated is thrust and a portion of the powergenerated is shaft horsepower. Such a convertible composite engine is tobe used in a compound aircraft, such as a compound helicopter in whichthe engine drives the helicopter rotor by shaft horsepower generationand in which the engine also drives a by-pass fan, or aircraftpropeller, in thrust generating operation. Such an engine, could also beused in a high speed aircraft in which the helicopter rotor was stowedduring the thrust generation mode of operation.

2. Description of the Prior Art Composite engines are not new but allpresently known composite engines include disadvantages or limitationswhich are overcome by our invention.

Rainbow U.S. Pat. No. 3,087,691 teaches a composite engine in which theengine exhaust gases are passed either through an exhaust nozzle forforward thrust generation or a free turbine for vertical thrustgeneration, however, the Rainbow configuration has a disadvantage of notbeing coaxial about the engine centerline and hence presents substantialfrontal area and other drag and weight creating problems.

Wilde U.S. Pat. No. 3,375,996 teaches a composite engine in which a freeturbine drives a by-pass fan for thrust generation mode of operation andwherein, diverter valves are used to drive a second free turbine, out ofalignment with the engine centerline, so as to drive a helicopter rotor.It will be noted that the Wilde construction again is not an in-lineengine concentric about the engine centerline and hence also presentsthe frontal area and drag and weight creating problems stated above.

Gist U.S. Pat. No. 3,381,47l also teaches a composite engine in which afree turbine drives a ducted fan and gases are bled from the fan duct topower a helicopter rotor driving free turbine. Again it will be notedthat this is not an in-line, concentric construction and hence presentsthe frontal area and other drag and weight creating problems alluded toabove.

Gist U.S. Pat. No. 3,375,997 shows an in-line composite engine which iscapable of thrust generating and shah horsepower operation, however, itis not a two-turbine configuration but rather a single turbineconfiguration in which brakes are used to cause one portion of theturbine to be stationary while the other portion rotates during one modeof operation and wherein other brakes are used to cause the secondportion of the turbine to be stationary while the first portion of theturbine rotates during the second mode of operation. Such a constructionhas two disadvantages in that enormously heavy brakes would be requiredto stop a turbine of the type which would be needed for aircraftoperation and, even then, the life of such a brake would be extremelyshort. Secondly, because the Gist configuration is actually a singleturbine, it would be impossible to use inlet guide vanes or divertervalves as the split-power control means since either would operate tocompletely shut-off flow through the turbine and thereby make the engineinoperative.

It will be noted that none of this prior art teaches a convertiblecomposite engine which is concentric about a single centerline and whichhas variable power splitting provisions between the thrust generatingand shaft horsepower modes of operation.

SUMMARY OF INVENTION A primary object of the present invention is toprovide an improved convertible composite engine which is capable ofoperating in either the thrust generating or shaft horsepower mode ofoperation and which is capable of producing from zero to I00 percentshafl horsepower output and zero to I00 percent thrust output singularlyor variable combinations of each output.

In accordance with the present invention, such a convertible compositeengine is provided in which the operating rotational speeds of thethrust creating fan free turbine and shaft horsepower creating freeturbine are variable, so that the fan speed is free to vary to satisfythrust requirements while the shaft horsepower generating power turbineis also free to maintain its selected speed.

It is a most important teaching of this invention that the enginecomponents are arranged concentrically along a single engine centerlineand thereby produce minimal frontal area and hence drag and weight.

It is another important feature of this invention that the powerturbines are concentric and in parallel flow relation to one another sothat full gas generator exhaust gas output can be passed selectivelythrough either free turbine or selectively partially through bothsimultaneously.

In accordance with another feature of this invention, the control of gasgenerator exhaust gas flow through the free turbines, and hence thesplit in power being generated by the free turbines, is controlled byvariable area inlet guide vanes at the inlet to each turbine.

It is still a further feature of our invention that our convertiblecomposite engine is functionally equivalent to two separate engines,namely a turbo-fan (or turbo-prop) engine and a turboshaft engine, andthe flexibility of separate engines is retained without the attendantcost, weight, installation and operational problems associated withseparate engines.

It is still a further feature of our engine that one gas generator isable to provide the gas energy needed to power the thrust generationdrive turbine and the shaft horsepower turbine either singularly or incombination, as desired.

It is still a further feature of our engine that when used in aircraftrequiring both thrust and shaft horsepower simultaneously, the enginepower limitations will not be exceeded since the sum of these two powerdemands is lower than the maximum power required in the pure thrust orpure shaft horsepower mode of operation.

According to a further feature of our invention, the exhaust gases beingdischarged to atmosphere through our thrust generanng drive turbine aredischarged through an inner duct and outlet, which may be fixed orvariable in cross-sectional area while the exhaust gases beingdischarged through our shaft horsepower generating free turbine aredischarged through a variable area exhaust outlet defined by a variablearea exhaust nozzle. The exhaust nozzle may be controlled so as to beinfinitely variable in position or may be of the twoposition variety inwhich the exhaust outlet is either fully opened or fully closed or mayalso be of the three-position variety in which the exhaust outlet iseither fully opened, fully closed, or in the cruise position wherein theexhaust outlet is partially open. In like manner, depending on theapplication of the engine, the inner duct area may be controlled, ifvariable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional showing ofthe convertible composite engine.

FIG. 2 is a perspective partial showing of a variable area inlet guidevane or nozzle ring illustrating apparatus for vary ing the position ofthe individual guide vanes simultaneously.

FIG. 3 is a schematic showing of the control for the composite engine.

FIG. 4 is a performance chart of engine operation during the shalthorsepower mode.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I we see theconvertible composite engine it) which is concentric about centerline oraxis 12. Engine case M envelopes most of the composite engine exceptbypass fan or compressor 16. Engine has forward end or inlet 18 andafter end or outlet 20. It will be noted that fan 16 is positionedforward of the inlet 22 of engine case 14 and is mounted for rotation soas to generate and pump compressed air in thrust generating fashionthrough annular passageway 24 which may be convergent and culminates infan discharge outlet 28 and which is defined between engine housing 14and fixed shroud 26. Support members 30 serve to support fixed shroud 26from engine case 14.

Gas generator 32 is located in the forward portion of engine casing 14and mounted for rotation concentrically about axis 12 and comprisescompressor section 34, combustion section 36 and turbine section 38. Theair which enters inlet 22 is compressed in passing through compressorsection 34, has heat added thereto in passing through combustion section36, has energy extracted therefrom in passing through turbine section 38in a sufficient amount so that turbine 38 drives compressor 34 throughconnecting shafiing 40. While gas generator 32 is illustrated to be ofthe single spool axial flow variety, it will be evident to those skilledin the art that it could be of the twin-spool axial variety, centrifugalflow, or other conventional gas generator configurations. Thepressurized and heated gases which are generated by gas generator 32 arethen pased through annular passage 42 to either or both free tur bines44 and 46. It will be noted that free turbines 44 and 46 are in parallelflow relation to one another so that the gases from the gas generator 32can be passed partially through both simultaneously or either totally asdesired. The gases which power free turbine 44 pass through apertures 48in the disc 50 of turbine 46 and then pass to atmosphere through theinner annular passageway 52 defined between tailcone or center body 54and exhaust duct 56. Although shown as fixed in FIG. I, exhaust duct 56may be variable similarly to 60. The gases which power free turbine 46are passed to atmosphere through the variable area, annular passage 58defined between exhaust duct 56 and variable area exhaust duct 60, whichconsisted in conventional fashion of a series of overlapping flapspivotally connected at pivot points 62 circumferentially about enginecasing 14. Support struts 64 support duct 56 and centerbody 54 fromengine case 14, which is in tum supported from the aircraft inconventional fashion.

Free turbine 44, which is the fan free turbine and shown to be of butnot limited to the two-stage variety, is mounted for rotationconcentrically about axis 12 and is connected by thru-shafi 66 to drivefan 16. Free turbine 46, which is the shaft horsepower generating freeturbine, includes rearwardly projecting drive or output shaft 68positioned concentrically about axis [2 and which carries bevel gear 70.Bevel gear 70 matingly engages bevel gear 72 of shaft horsepowertake-ofi means 74, which is typically operatively connected inconventional fashion to drive helicopter rotor drive shaft 78 and hencehelicopter rotor 76.

It is important to note that fan [6, gas generator 32, free turbines 44and 46 are positioned in axial alignment along axis 12 and are mountedfor rotation concentrically thereabout through conventional bearingsupport means. All other portions of engine 10 are also concentric withrespect to axis 12, including fixed shroud 26, engine case 14,centerbody 54, fixed exhaust duct 56, and variable area exhaust duct 60.

A ring of variably positionable inlet guide vanes 80 and 82, or othervariable geometry mechanism, are positioned at the inlet to freeturbines 44 and 46, respectively, and may be operated in any manner,such as is shown in FIG. 2 and to be described hereinafter, so as toprovide a variable area inlet to the free turbines 44 and 46.Accordingly. the exhaust gases from gas generator 32 can pass throughfree turbine 44 exclusively when inlet guide vanes 80 are open and inletguide vanes 82 are closed-01f. When in this condition, the engine isoperating entirely in thrust mode of operation with free turbine 44driving by-pass fan 16. Further, with inlet guide vanes closed off andinlet guide vanes 82 open, all of the gas generator exhaust gases passthrough free turbine 46 so that the convertible composite engine 10 isthen operating in the shaft horsepower mode of operation which, in thisinstance, is the helicopter mode of operation. With variable area inletguide vanes 80 and 82 at selected intermediate positions, the amount ofexhaust gas from the gas generator 32 being passed through free turbines44 and 46 can be accurately controlled, and in this fashion, the powersplit between the turbines 44 and 46 can be controlled.

As best shown in FIG. 2, inlet guide vanes 80 or 82, which extend in aring concentrically about axis 12 in annular gas flow passage 42, can befabricated and actuated in any convenient manner. For example, the vanes80, or 82, can be pivotally connected at pivot points 84 to fixed ring86 and pivotally connected at pivot points 88 and 91 to movable rings 93and 95 so that, as rings 93 and 95 are caused to Valve in oppositedirections, conceivably through pilot operated hand lever 97 connectedthereto by conventional mechanism 99, the variable inlet guide vanes, 80or 82, can be caused to change position in unison and thereby vary thearea of the inlet to turbines 44 and 46 from a fully closed to a fullyopen position and all intermediate positions therebetween. It willtherefore be seen that, due to the parallel flow orientation betweenturbines 44 and 46, all of the exhaust gas from gas generator 32 can bepassed through turbine 44 for complete thrust generating mode operation,all of the exhaust gases can be passed through turbine 46 for completeshaft horsepower mode of operation and, with the inlet guide vanes 80and 82 in intermediate positions, a power sharing or splitting of theexhaust generated gases occurs between the turbines so that par tialthrust generation and partial shaft horsepower operation isaccomplished.

The variable area inlet guide vanes 80 and 82 not only accomplish theaforementioned power splitting function but also maintain high turbineefiiciencies during power-split operations by varying the turbine inletnozzle areas to optimize the angle and flow velocity of the gases fromgas generator 32 entering the turbines 44 and 46.

Referring to FIG. 3 we see our engine control or fuel control 90, whichserves to control fuel flow to the gas generator 32 and to positioninlet guide vanes 80, 82 and variable area exhaust nozzle 60. Control 90consists of gas generator fuel metering or control valve 92, which ispositioned by multiplier 94 and lever and is located in fuel line 96 toregulate the flow of fuel from fuel tank 98 to the gas generator 32. 18392 is essentially a limiting valve and serves to protect the gasgenerator 32 so that it does not exceed its safe operating limits. Theposition of valve 92 is determined, in concert with other meanshereinafter described, by gas generator condition lever l00, which actsthrough cam 102 and pivot link I04 to impose a load upon positioningspring 106 of ilyball governor I08. Governor 108 has a gas generatorspeed N, responsive load imposed thereon in opposition to spring 106 soas to position the roller members of multiplier 94. This gas generatorspeed N, input is imparted to positioning spring 106 since ilyballgovernor 108 is driven as a function of gas generator speed N, by inputgear 1 [0 which is operatively connected to be driven at or as afunction of gas generator speed N,.

Computer actuator [12, of conventional design, is programmed to limitthe positioning of fuel flow valve 92 so as to cause gas generator 32 toremain within its surge, speed and temperature limits, and receives agas generator inlet temperature signal from line 4. Computer actuator112 positions multiplier 94 with the control limit signal which islimiting fuel flow, (W divided by compressor discharge pressure, CDP, or(W/CDP) limit. The parameter compressor discharge pressure (CD?) is fedto multiplier 94 through signal line 1 [6 to computer actuator 118which, in turn, positions pivot lever 120 so that the net inputpositioning signal to gas generator fuel valve 92 is then gas generatorfuel flow limit illie-tr- Shaft horsepower turbine fuel control valveI22 serves to control fuel flow therethrough from fuel tank 98 to gasgenerator 32, through valve 92, as a function of shaft horsepowerturbine 46 requirement and within the overall limit established by valve92, as hereinbefore described. The shaft horsepower free turbine 46rotational speed N causes governor 132 to rotate at or as a function ofturbine 46 speed by causing input drive member 134 to rotate at thatspeed. The shaft power turbine speed selector lever 124, which actsthrough cam I26 and pivot link I28, imparts a positioning force tospring I30 in opposition to free turbine 46 speed responsive positioningforce imparted thereto by flyball governor 132 so as to establish aselected flyball governor 132 rotational speed.

Changes in flyball governor I32 rotational speed, caused by varyingshaft horsepower loads on the free turbine 46, reposition the meteringvalve I22 providing the gas generator 32 with fuel flow as a function ofshaft horsepower demanded from the power turbine 46. This operation isknown as "closed loop feedback or "demand" type of gas turbine enginecontrol typical of conventional turbo-shaft engines.

Fan turbine 44 is controlled by fan turbine fuel metering or controlvalve 140, which is positioned in fuel line 142 in parallel with valve122 in fuel line 144 so as to provide fuel flow from fuel tank 98therethrough to gas generator 32 as a function of the position thereof.The position of fan turbine fuel flow metering valve I40 is determinedby the position of pilot operated fan turbine lever I46, which imparts apositioning force to valve 140 through overriding spring I48. Lever I46,therefore, directly controls the fuel entering gas generator 32, withinthe overall limit established by valve 92, and the fan thrust developedby the convertible composite engine 10. This operation is known as"direct" or open loop" type of gas turbine engine control typical ofconventional turbofan or turbojet engines. Override lever I50, pivotallysupported at pivot point I52 is positioned by metering valve I22 throughlink I54 to permit valve I22 to transmit the amount of fuel required bythe shaft power turbine 46 regardless of the fuel setting of meteringvalve I40. Override lever 150 thus acts as a variable limit on fan fuelvalve 140 so that in the competition between it and shaft fuel valve I22for a proportionate part of the total fuel flow permitted by limitingvalve 92, valve 122 always takes precedence. It is noted that thispreferential treatment is provided in anticipation of the use of thisconvertible composite engine in a compound helicopter where adequatepower to the lifting rotor in preference to the forward propulsion fanis mandatory. In other applications, override lever 150 may be deletedor applied oppositely.

It is very important to note that fan valve I40 is connected throughsignal amplifier I56 to conventional actuator mechanism I58, which maybe hydraulically, electrically, or pneumatically actuated inconventional fashion to position the various vanes of variable areainlet guide vane ring 80 as a function of the position of fan fuelcontrol valve 140 and hence fuel flow therethrough. In similar fashion,shaft horsepower valve I22 is connected through signal amplifier I60through conventional actuator mechanism I62 to position the variousvanes of variable area inlet guide vane ring 82 as a function of theposition of shaft horsepower valve I22, and hence is a function of thefuel flow to the gas generator therethrough.

It should further be noted that pivot link 164 and selectively contouredcam I66 are positioned by shaft horsepower valve I22 and work throughsignal amplifier I68 to position variable area exhaust duct or nozzle 60through conventional actuators I70, which may be of the electrical,hydraulic or pneumatic variety and serve to cause the overlapping flapsof nozzle 60 to pivot about their support pivot points 62 to vary thearea of passage 58.

Fuel regulators I72 and I74 serve in conventional fashion to regulatethe fuel pressure drop across valves I22 and 140, and valve 92,respectively. and cause excess fuel to be bypassed back to the inlet ofpump I82 through by-pass fuel lines 176 and 178, respectively, so thatthe fuel flow through these valves is directly proportional to valveposition since the position of the valves determines the area of themetering orifices which the valves define.

OPERATION OF CONTROL To demonstrate the operation of control 90, it willnow be described as controlling convertible composite engine I0 of thetype shown in FIG. I in which power turbine 44 drives the thrustgenerating fan 16 and power turbine 46 drives the helicopter rotor 76.

To start the engine, speed selector lever 124 is first placed in itsground idle position I89. This causes the fuel metering valve 122 andthe power turbine variable inlet guide vanes 82 to move into theirground idle position and also causes the variable exhaust nozzle toassume position 60b. While a flow of fuel when established is now ableto pass through metering valve I22, actual fuel flow to the engine isdependent upon actuation of gas generator lever I00. Placement of leverin its ground idle position 180, imposes a positioning force on springI06, which will eventually be balanced by the gas generator speed N,feedback force which drives speed responsive governor I08. Lever 100, inthis fashion, serves to position gas generator fuel metering valve 92.An engine starter, not shown but conventional in design, serves to turnover gas generator 32 and drive fuel pump I82. Conventional ignitionmeans are used to ignite the fuel within combustion section 36 of gasgenerator 32 with the fuel being introduced thereinto from fuel tank 98through pump I82, fuel pressure regulator I72, shaft horsepower valve122, which is positioned to admit the required amount of fueltherethrough during engine starting, through fuel pressure regulator I74and gas generator fuel regulating valve 92 into the combustion section36 of gas generator 32 in conventional fashion. With the engine ignitedand operating at idle condition, the engine per se now serves to drivefuel pump 182.

In this description, it should be understood that the placement of speedselector lever I24 in its start position I89 may be accomplishedmanually or automatically by an interlock arrangement (not shown), orequivalent, with gas generator lever I00 during the starting sequence.

For take-off, the helicopter mode of aircraft operation is used. To makeavailable the shaft horsepower required by the helicopter rotor, theshaft power turbine speed selector lever 124 may be set at an operatingposition, such as station I86, and gas generator condition lever I00 ispositioned at its full open or maximum position at station I88. Duringthe starting operation and this take-off condition, fan lever 146 ispositioned such that fan fuel control valve 140 and inlet guide vanes 80are in their fully closed position. The positioning of the power turbinespeed selector lever 124 at the station 186 position serves to open thevariable exhaust nozzle to position 60a, and shah horsepower meteringvalve I22 and inlet guide vanes 82 as previously described such thatfuel is being regulated through valve 122 and provided to gas generator32 as a function of valve 122 position. The operation of gas generator32, with inlet guide vanes 82 in their open position, will serve todrive free turbine 46, which in turn drives helicopter rotor 76, whichis in its minimum pitch, minimum power condition.

When the helicopter rotor comes up to speed, rotor blade pitch isincreased to take work out of the helicopter rotor and this serves toreduce the speed of the helicopter rotor and the shaft horsepower freeturbine 46. From an operation standpoint, it can be considered that theengine has been operating as shown on the engine operation chart in FIG.4 along minimum speed line 200 which for purposes of this description isunderstood to coincide with lever position I86. As stated above,increasing the helicopter rotor blade pitch causes helicopter rotor andfree turbine 46 speed to be reduced. Due to the shaft horsepower freeturbine speed N feedback to speed responsive governor I32 via drive I34,governor 132 and spring act to reposition regulating valve 122 so as toincrease fuel flow therethrough to gas generator 32. The efi'ect is tobring engine operation into a stablized condition along minimum speedline 200 at the shah: horsepower level required by the power turbine 46.With shaft horsepower fuel regulating valve 122 in this new position,valve 122 is doing the regulating of the fuel flow between fuel tank 98and gas generator 32. The gas generator fuel regulating valve 92 is notserving to regulate fuel flow in this helicopter mode of operation,unless one of the gas generator parameters being controlled thereby,such as speed or temperature, exceeds its preselected computer setting.If the speed selector lever 124 had been moved to position 190 in FIG.3, corresponding to maximum shaft power turbine governed speed setting,the engine would have operated along line 220 shown in FIG. 4. Ourcontrol 90 can well be used with conventional automatic speed resetfeatures which are not disclosed herein since they are not considered tobe a part of this invention, but these conventional systems whenutilized with our disclosed fuel control system would add automaticultimate positioning of shaft horsepower fuel regulating valve 122 tomaintain constant power turbine 46 rotational speed, as established bythe position of speed selector lever 124. for all levels of shafthorsepower demanded from the power turbine 46 by the helicopter rotor.

initiation of fan thrust required to transition the aircraft to fan modeof operation is accomplished by actuating lever 146 to open fan turbinefuel regulating valve 140 and inlet guide vanes 80 to a selectedposition so that gas generator 32 is receiving fuel from tank 98 throughparallel fuel regulating valves I22 and 140 simultaneously. During thistransition period, we are operating partially in the helicopter mode andpartially in the thrust mode and the gas power of the gas generator 32is being split between the free turbines 44 and 46. In this transitoryor two-mode operation, the demands of helicopter rotor 76 continue todictate the position of fuel regulating valve 122 and the position ofpilot operated lever I46 continues to regulate the position of fan fuelmetering valve I40 so that the total amount of fuel being passed throughboth valves is being provided to the gas generator 32 through gasgenerator fuel regulating valve 92. Regulating valve 92, however, willserve to insure that the operating limits of the gas generator 32 arenot exceeded due to the joint demands of the fan 16 and the rotor 76.Also, as previously explained, overriding lever I50 prevents excessiveinputs to the fan turbine fuel metering valve 140 from limiting theability of fuel metering valve [22 to meet the fuel (power) demands ofpower turbine 46. it is to be understood, however, that as the aircrafttransitions from take off or hover into forward flight, the requirementof rotor 76 for power and fuel diminishes thus reducing the restrictionby override lever 150 on the amount of fuel passed by fan fuel valve140.

As previously explained, the position of variable area exhaust nozzle 60is determined by the position of shaft horsepower fuel regulating valve122. During the engine starting operation, lever [24, and therefore,valve 122 and variable inlet guide vanes 82, is placed in ground idle189 position and the exhaust nozzle 60 assumes the partially open cruiseposition 60b. Actual fuel flow to the engine is initiated when lever 100is moved out of off position. When the engine is operating in the pureshaft horsepower mode, such as for take off, the variable area nozzle isin the fully open position 60a. When the engine is operating in cruisecondition, the variable area nozzle is in its intermediate or cruiseposition 60b. If the aircraft is to be operated fully in the fan modewith the rotor 76 of the helicopter stopped or stowed, the power turbinespeed selector lever l24 would be moved to its shut-off position so asto stop fuel flow through shalt horsepower fuel regulating valve 122,close off inlet guide vanes 82 and move exhaust nozzle to its closedposition 60 c, and engine would be controlled through lever 146 toposition valve 140 and drive free turbine 44 as a function of lever 146position.

While we have disclosed a control in which the area of the variable areaexhaust nozzle 60 is controlled as a function of the position of thefuel flow regulating valves 122 and 140, it

will be evident to those skilled in the art that the area of the exhaustmale 60 could have been controlled in a variety of other ways, forexample, as a function of the relative position of the inlet guide vanesof the two free turbines or as a function of the total pressure of theengine air flow in the area just upstream of the inlet guide vanes ofthe two free turbines, both by the use of conventional mechanisms. Boththe relative positions of the free turbine inlet guide vanes and therelative total pressures upstream thereof is determined by and henceresponsive to fuel control 90.

When we are operating in the pure thrust mode of operation, ourconvertible composite engine 10 is being controlled by an "open loop"direct-control system.

As previously explained, this means the pilot of the aircraft direcflycontrols the power (thrust) output of his engine without regard for itsinternal conditions except for conventional endurance and safety limitsby direct control of fuel flow.

When we are in the pure shaft horsepower or helicopter mode of engineoperation, engine 10 is controlled by a closed loop feedback" powerdemand control system. Also as previously explained, this means that thepilot sets the governor 132, that controls the nominal rotative speed ofthe engine output shaft to the helicopter rotor, to the desiredoperating speed and the engine automatically responds to changes inpower demand imposed by the pilot via conventional aircrafi flightcontrols to maintain the rotor system at the original nominal speedsetting.

When the vehicle powered by our convertible composite engine [0 is inthe helicopter mode of operation, the vehicle is controlled by aconventional helicopter flight control system which form no part of thisinvention. The engine control system taught herein operatesindependently of the helicopter flight control system except asdescribed above. Similarly, when the vehicle is in pure thrust, fixedwing mode of operation, vehicle flight control is accomplished byconventional fixed wing flight controls which form no part of thisinvention and which are independent of the engine control system 90taught herein. It is important to understand that, consequently, thisengine presents no unconventional engine or aircraft controls to thepilot, that it can be operated in pure thrust or pure shaft power modesor any proportion of both, that transfer from one mode to the other oroperation at either mode or combination is smooth and requires nounusual or unconventional levers or manipulations, and that no specialtraining is required for an average pilot to use them.

We wish it to be understood that we do not desire to be limited to theexact details of construction shown and described, for obviousmodifications will occur to a person skilled in the art.

We claim:

1. A convertible engine having an axis and including:

A. a gas generator comprising a compressor, a burner, and a turbine, andwith said compressor and turbine mounted for rotation about said axis,

8. two free turbines positioned downstream of the gas generator andmounted for independent rotation about said axis and being in parallelflow relationship with the gas generator.

2. Apparatus according to claim I and including means operativelyconnected to be driven by one of the free turbines during one mode ofoperation and means operatively connected to be driven by the other freeturbine in a second mode of operation.

3. Apparatus according to claim 2 and including means to selectivelycontrol the flow of exhaust gas from the gas generator through each ofthe free turbines.

4. Apparatus according to claim 3 and including a fixed or variablegeometry exhaust duct operatively connected to one of the free turbinesand a variable area exhaust duct operatively connected to the other freeturbine.

5. A convertible composite engine capable of combination shafthorsepower and direct thrust mode of operation and having an axis andincluding:

A. a gas generator mounted for rotation about said axis,

B. two free turbines mounted for independent rotation about said axisand positioned downstream of said gas generator so as to be powered bythe exhaust gases therefrom and further positioned so as to be inparallel flow relationship with one another,

C. means operatively connecting one of said free turbines to a directthrust generating device,

D. means operatively connecting the other of said free turbines to ashaft horsepower driven device,

E. and means operative to divide gas generator exhaust gas flow betweensaid free turbines.

6. Apparatus according to claim wherein said exhaust gas flow dividingmeans are variable area inlet guide vanes at the inlet of each of saidfree turbines and separate exhaust gas ducts for said free turbines.

7. A convertible composite, in-line engine extending along an axis andincluding: A. a gas generator comprising a compressor, a burner, and aturbine, and with said compressor and turbine mounted for rotation aboutsaid axis, B. a first free turbine mounted for rotation about said axisand positioned downstream of the gas generator to receive exhaust gasestherefrom, C. a second free turbine mounted for rotation about said axisand positioned downstream of said gas generator to receive exhaust gasestherefrom and also positioned in parallel flow relationship to saidfirst free turbine, D. a first power generating device connected to bedriven by the one of said free turbines, E. a second power generatingdevice connected to be driven by the other of said free turbines, F. andmeans to vary the amount of gas generator exhaust gas being passedthrough either of said free turbines without afi'ecting the powerdeveloped by the other of said free turbines.

8. Apparatus according to claim 7 wherein said exhaust gas glow varyingmeans constitute variable area inlet guide vanes operatively associatedwith each of said first and second free turbines.

9. Apparatus according to claim 8 wherein the blades of said second freeturbine are located at a greater diameter from said axis than the bladesof said first free turbine and so that the gas path flow therethrough isconcentric about said axis and so that each turbine exhausts throughseparate exhaust ducts.

10. Apparatus according to claim 9 wherein said first power generatingmeans is a helicopter rotor operatively connected to be driven by saidsecond free turbine and wherein said second power generating means is aby-pass fan compressor operatively connected to be driven by said firstfree turbine.

ll. A convertible composite, in-line, axial flow engine having an axisand including:

A. pressurized gas generating means comprising, a compressor, a burner,and a turbine, and with said compressor and turbine mounted for rotationabout said axis,

B. two free turbines mounted for rotation concentrically about said axisand positioned downstream of said gas generating means to receive and bedriven by the gases therefrom and having turbine blade paths ofdifferent diameters and with the free turbines being in parallel flowrelation,

C. first power take-off means connected to be driven by one of said freeturbines,

D. second power take-off means connected to be driven by the other ofsaid free turbines,

E. means to regulate the amount of pressurized gas flow from saidpressurized gas generating means through each of said free turbines.

12. Apparatus according to claim II and including engine housing meansdefining an annular passage between said gas generator and to andthrough said free turbines and with each of said free turbinesexhausting through separate exhaust ducts.

13. Apparatus according to claim 12 and including a variable areaexhaust outlet positioned downstream of one of said free turbines toreceive gas flow therefrom for discharge therethrough to atmosphere anda fixed or variableoutlet positioned downstream of the other of saidfree turbines to receive gas flow therefrom for discharge therethroughto atmosphere.

14. A convertible composite, in-line engine having a single centerlineand including:

A. an engine case having a forward end and an after end and positionedconcentrically about the centerline,

B. a by-pass fan compressor consisting of at least one stage positionedforward of the engine case and mounted for rotation about thecenterline,

C. a gas generator positioned within the engine case at the forwardportion thereof and mounted for rotation about the centerline andincluding:

1. a compressor section communicating with the inlet of the engine case,

2. a combustion chamber section communicating with the compressorsection to receive compressed air therefrom to be heated therein,

3. a turbine section positioned aft of and in communication with thecombustion section so as to be rotatably driven by the heated compresorgases discharged therefrom and connected to the compressor section todrive the compressor section,

D. a free turbine positioned aft of the gas generator so as to bepowered by the exhaust gas therefrom and mounted for rotation about thecenterline and operatively connected to drive the by-pass fan duringengine thrust generation mode of operation,

E. a second free turbine positioned aft of the gas generator to receiveexhaust gases therefrom to be driven thereby and mounted for rotationabout the centerline and also positioned in parallel flow relationshipto said first free turbine,

F. shaft horsepower take-off means operatively connected to the secondfree turbine to be operatively driven thereby during the shafthorsepower mode of operation,

G. means to vary the amount of gas generator exhaust gases being passedthrough either of said free turbines without affecting the powerdeveloped by the other of said free turbines.

15. Apparatus according to claim l4 and including:

A. a fixed exhaust duct positioned aft of said first free turbine andcommunicating therewith so that the exhaust gases passing through thefirst free turbine will be discharged to atmosphere through the fixedexhaust duct, and

B. a variable area exhaust duct operatively connected to the second freeturbine and communicating therewith so that the exhaust gases beingpassed through the second free turbine to power that turbine will beexhausted to atmosphere therethrough.

16. Apparatus according to claim 15 wherein said first free turbineincludes at least one stage of rotatable turbine blades mounted at aselected diameter for rotation about the centerline and wherein thesecond free turbine includes at least one stage of turbine bladesmounted for rotation about the centerline at a diameter greater than thediameter of the blades of the first free turbine and wherein the gasespowering the first free turbine pass through appropriate apertures inthe support disc of the second free turbine.

17. Apparatus according to claim 16 and including a fixed shroudenveloping said by-pass fan compressor and cooperating with said enginecase to define an annular exhaust passage for the fan generatedcompressed air to effect thrust generation.

. I I t i

1. A convertible engine having an axis and including: A. a gas generatorcomprising a compressor, a burner, and a turbine, and with saidcompressor and turbine mounted for rotation about said axis, B. two freeturbines positioned downstream of the gas generator and mounted forindependent rotation about said axis and being in parallel flowrelationship with the gas generator.
 2. Apparatus according to claim 1and including means operatively connected to be driven by one of thefree turbines during one mode of operation and means operativelyconnected to be driven by the other free turbine in a second mode ofoperation.
 2. a combustion chamber section communicating with thecompressor section to receive compressed air therefrom to bE heatedtherein,
 3. a turbine section positioned aft of and in communicationwith the combustion section so as to be rotatably driven by the heatedcompressor gases discharged therefrom and connected to the compressorsection to drive the compressor section, D. a free turbine positionedaft of the gas generator so as to be powered by the exhaust gastherefrom and mounted for rotation about the centerline and operativelyconnected to drive the by-pass fan during engine thrust generation modeof operation, E. a second free turbine positioned aft of the gasgenerator to receive exhaust gases therefrom to be driven thereby andmounted for rotation about the centerline and also positioned inparallel flow relationship to said first free turbine, F. shafthorsepower take-off means operatively connected to the second freeturbine to be operatively driven thereby during the shaft horsepowermode of operation, G. means to vary the amount of gas generator exhaustgases being passed through either of said free turbines withoutaffecting the power developed by the other of said free turbines. 3.Apparatus according to claim 2 and including means to selectivelycontrol the flow of exhaust gas from the gas generator through each ofthe free turbines.
 4. Apparatus according to claim 3 and including afixed or variable geometry exhaust duct operatively connected to one ofthe free turbines and a variable area exhaust duct operatively connectedto the other free turbine.
 5. A convertible composite engine capable ofcombination shaft horsepower and direct thrust mode of operation andhaving an axis and including: A. a gas generator mounted for rotationabout said axis, B. two free turbines mounted for independent rotationabout said axis and positioned downstream of said gas generator so as tobe powered by the exhaust gases therefrom and further positioned so asto be in parallel flow relationship with one another, C. meansoperatively connecting one of said free turbines to a direct thrustgenerating device, D. means operatively connecting the other of saidfree turbines to a shaft horsepower driven device, E. and meansoperative to divide gas generator exhaust gas flow between said freeturbines.
 6. Apparatus according to claim 5 wherein said exhaust gasflow dividing means are variable area inlet guide vanes at the inlet ofeach of said free turbines and separaTe exhaust gas ducts for said freeturbines.
 7. A convertible composite, in-line engine extending along anaxis and including: A. a gas generator comprising a compressor, aburner, and a turbine, and with said compressor and turbine mounted forrotation about said axis, B. a first free turbine mounted for rotationabout said axis and positioned downstream of the gas generator toreceive exhaust gases therefrom, C. a second free turbine mounted forrotation about said axis and positioned downstream of said gas generatorto receive exhaust gases therefrom and also positioned in parallel flowrelationship to said first free turbine, D. a first power generatingdevice connected to be driven by the one of said free turbines, E. asecond power generating device connected to be driven by the other ofsaid free turbines, F. and means to vary the amount of gas generatorexhaust gas being passed through either of said free turbines withoutaffecting the power developed by the other of said free turbines. 8.Apparatus according to claim 7 wherein said exhaust gas glow varyingmeans constitute variable area inlet guide vanes operatively associatedwith each of said first and second free turbines.
 9. Apparatus accordingto claim 8 wherein the blades of said second free turbine are located ata greater diameter from said axis than the blades of said first freeturbine and so that the gas path flow therethrough is concentric aboutsaid axis and so that each turbine exhausts through separate exhaustducts.
 10. Apparatus according to claim 9 wherein said first powergenerating means is a helicopter rotor operatively connected to bedriven by said second free turbine and wherein said second powergenerating means is a by-pass fan compressor operatively connected to bedriven by said first free turbine.
 11. A convertible composite, in-line,axial flow engine having an axis and including: A. pressurized gasgenerating means comprising, a compressor, a burner, and a turbine, andwith said compressor and turbine mounted for rotation about said axis,B. two free turbines mounted for rotation concentrically about said axisand positioned downstream of said gas generating means to receive and bedriven by the gases therefrom and having turbine blade paths ofdifferent diameters and with the free turbines being in parallel flowrelation, C. first power take-off means connected to be driven by one ofsaid free turbines, D. second power take-off means connected to bedriven by the other of said free turbines, E. means to regulate theamount of pressurized gas flow from said pressurized gas generatingmeans through each of said free turbines.
 12. Apparatus according toclaim 11 and including engine housing means defining an annular passagebetween said gas generator and to and through said free turbines andwith each of said free turbines exhausting through separate exhaustducts.
 13. Apparatus according to claim 12 and including a variable areaexhaust outlet positioned downstream of one of said free turbines toreceive gas flow therefrom for discharge therethrough to atmosphere anda fixed or variable outlet positioned downstream of the other of saidfree turbines to receive gas flow therefrom for discharge therethroughto atmosphere.
 14. A convertible composite, in-line engine having asingle centerline and including: A. an engine case having a forward endand an after end and positioned concentrically about the centerline, B.a by-pass fan compressor consisting of at least one stage positionedforward of the engine case and mounted for rotation about thecenterline, C. a gas generator positioned within the engine case at theforward portion thereof and mounted for rotation about the centerlineand including:
 15. Apparatus according to claim 14 and including: A. afixed exhaust duct positioned aft of said first free turbine andcommunicating therewith so that the exhaust gases passing through thefirst free turbine will be discharged to atmosphere through the fixedexhaust duct, and B. a variable area exhaust duct operatively connectedto the second free turbine and communicating therewith so that theexhaust gases being passed through the second free turbine to power thatturbine will be exhausted to atmosphere therethrough.
 16. Apparatusaccording to claim 15 wherein said first free turbine includes at leastone stage of rotatable turbine blades mounted at a selected diameter forrotation about the centerline and wherein the second free turbineincludes at least one stage of turbine blades mounted for rotation aboutthe centerline at a diameter greater than the diameter of the blades ofthe first free turbine and wherein the gases powering the first freeturbine pass through appropriate apertures in the support disc of thesecond free turbine.
 17. Apparatus according to claim 16 and including afixed shroud enveloping said by-pass fan compressor and cooperating withsaid engine case to define an annular exhaust passage for the fangenerated compressed air to effect thrust generation.